The art of reducing the unpleasant and at times dangerous roll motion of boats and ships in waves have evolved over many years, and there are many principle technologies used with varying benefits and results for different conditions, type of watercraft and not least cost of implementation and operation. Such different systems include fin stabilizers, gyro stabilizers and bilge tanks to mention the most common ones.
The traditional stabilization systems used in passenger vessels, naval vessels etc., were generally designed for use in underway situations and mostly for boats cruising in displacement mode and thereby in relatively low velocities. The watercraft that have traditionally been using stabilizers have also by their size and hull shapes generally had long roll times, thereby requiring relatively slow acting stabilization system, where counter forces are applied to the waves forces over relatively long time periods. Over the last 15 years, the market has evolved to where there is a requirement for also providing roll stabilization when the watercraft is at anchor, i.e. not having any forward motion, as well as stabilization systems being installed in much faster boats, including planning boats. These changes create many new challenges and issues, as explained below.
The first of the generally known issues is that with the watercraft not moving forward through the water, thus being able to make use of the forces in the waterflow passing the fins by the forward motion of the vessel to create a force to counter the waves forces that rolls the watercraft, the only way a fin stabilizer can apply a counter force, is to flap/swim the fins. This means that both the peak force possible as well as the time such a force can be applied is limited. The force is a result of the size of fin and the speed the fin is moved, and as an opposite, the faster the fin is moved, the shorter a time period the force can be applied as there is a limited physical movement of the fin, and it also has to be stopped without causing too much counter force in the undesired direction at the time. Mathematically or as a term in physics, the total force impulse is in principally determined by the fin size.
The second issue generally is the fact that modern faster watercrafts have a
hull shape and a weight that makes their natural roll periods a lot shorter than the traditional vessels where stabilizers have been installed, and also that their physical requirement for stabilizer force is a higher factor compared to the boat size in comparison with the traditional watercraft equipped with stabilizers. The principal mathematical way to calculate the necessary force of a stabilizing system to reduce the roll by a desired amount is mostly based on a factor called Metacentric height (GM). This is a factor decided by how stiff the watercraft is on the water, i.e. the more it follows the waves angles, the more force is required from the stabilizer system to counter this roll, and what a stabilizer system actually does, is to force the boat to not follow the waves angle.
Given the fact that these modern vessels both require more force, while also allowing a shorter period to apply this force, it is apparent that these vessels are much more difficult to stabilize.
The simple solution is to install very big fins to be able to reach the desired roll reduction force, however this is not always a very good solution for several reasons, not least because very big fins cause a lot of drag through the water and thereby cause increased fuel consumption and reduced speed, more important on fast vessel given that drag as everything is a quadratic factor of velocity, ^2 so the impact becomes big on fast watercrafts. The physical sizes and power consumption of the actuating units required to run larger fins also create considerable problems as modern watercraft are designed with a high priority on available living space and cost efficiency.
As evidenced by other patents and work over the last years, much effort have been put into creating fins with low drag, and powering, systems that are as cost and energy efficient as possible.
However, a third issue that evidently have not been considered so much, but is an important benefit in this invention, is that by using very large traditional fins to reach the desired roll reduction forces, this will also have other impacts on the vessels, the faster and lighter the watercraft, the more negative these impacts become. A watercraft have 6 degrees of motion freedom in water, simply increasing the traditional force impulse will cause other negative effects on the watercraft by causing increased sway and yaw, both in underway and in at anchor situations which are then other, but still uncomfortable and negative effects on the boat.
At present, the overall market view is that fin stabilizers, even with the limitations of present fins, provide the overall best solutions as a single technology system to use for both underway and at anchor stabilization as most other solutions, like gyros or stabilization tanks, do not perform very well in underway situation of
faster vessels. However, the problem of being able to apply enough force in at anchor situation, or at high speed with light weight vessels, without causing too many other negative implications on the watercraft in general still remains to be solved for fin stabilizers.
One solution to improve this situation is presented in patent US 2007/0272143/EP 1 577 210 that describes stabilizer fins that have the ability to change its size and shape to thereby have different size in underway and at anchor situations, increasing the possible force without causing additional drag when not needed.
European patent application EP1577210A1, describes an active roll stabilization system comprising fins with a sub-elements, where the sub elements are movable, i.e. linked with respect to the fins.
Other known solutions are retractable stabilizer fins that are only deployed into the water when needed, thereby creating no drag when not needed.
Both of these solutions are rarely used in watercraft with limited installation space and budgets due to their complexity, internal space requirements and cost.
There are also many other patents and patent applications for various means and methods to increase the efficiency of fin stabilizers, most of these relate to various types of drive mechanism or control algorithms and are thereby unrelated to the invention.